linux-kernel - Re: [PATCH v2 3/7] KVM-HV: KVM Steal time implementation

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Message-ID: <4DFDC821.2090905@redhat.com>
Date:	Sun, 19 Jun 2011 12:57:53 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Glauber Costa <glommer@...hat.com>
CC:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	Rik van Riel <riel@...hat.com>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Anthony Liguori <aliguori@...ibm.com>,
	Eric B Munson <emunson@...bm.net>
Subject: Re: [PATCH v2 3/7] KVM-HV: KVM Steal time implementation

On 06/17/2011 01:20 AM, Glauber Costa wrote:
> To implement steal time, we need the hypervisor to pass the guest information
> about how much time was spent running other processes outside the VM.
> This is per-vcpu, and using the kvmclock structure for that is an abuse
> we decided not to make.
>
> In this patchset, I am introducing a new msr, KVM_MSR_STEAL_TIME, that
> holds the memory area address containing information about steal time
>
> This patch contains the hypervisor part for it. I am keeping it separate from
> the headers to facilitate backports to people who wants to backport the kernel
> part but not the hypervisor, or the other way around.
>
>
>
> +#define KVM_STEAL_ALIGNMENT_BITS 5
> +#define KVM_STEAL_VALID_BITS ((-1ULL<<  (KVM_STEAL_ALIGNMENT_BITS + 1)))
> +#define KVM_STEAL_RESERVED_MASK (((1<<  KVM_STEAL_ALIGNMENT_BITS) - 1 )<<  1)

Clumsy, but okay.

> +static void record_steal_time(struct kvm_vcpu *vcpu)
> +{
> +	u64 delta;
> +
> +	if (vcpu->arch.st.stime&&  vcpu->arch.st.this_time_out) {

0 is a valid value for stime.

> +
> +		if (unlikely(kvm_read_guest(vcpu->kvm, vcpu->arch.st.stime,
> +			&vcpu->arch.st.steal, sizeof(struct kvm_steal_time)))) {
> +
> +			vcpu->arch.st.stime = 0;
> +			return;
> +		}
> +
> +		delta = (get_kernel_ns() - vcpu->arch.st.this_time_out);
> +
> +		vcpu->arch.st.steal.steal += delta;
> +		vcpu->arch.st.steal.version += 2;
> +
> +		if (unlikely(kvm_write_guest(vcpu->kvm, vcpu->arch.st.stime,
> +			&vcpu->arch.st.steal, sizeof(struct kvm_steal_time)))) {
> +
> +			vcpu->arch.st.stime = 0;
> +			return;
> +		}
> +	}
> +
> +}
> +
>
> @@ -2158,6 +2206,8 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
>   			kvm_migrate_timers(vcpu);
>   		vcpu->cpu = cpu;
>   	}
> +
> +	record_steal_time(vcpu);
>   }

This records time spent in userspace in the vcpu thread as steal time.  
Is this what we want?  Or just time preempted away?


-- 
error compiling committee.c: too many arguments to function

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